Convertible AC is probably just one with a variable speed compressor. Ideally, your room should be cooled effectively with a 1 ton unit. However, the amount of glass area (windows), whether you can use heavier curtains and other factors (target temp, outside temp, humidity, number of people / other heat source in the cooled space, usage pattern, i.e., day vs night, outdoor unit placement, even distance from indoor to outdoor unit) affects cooling performance.
I'll try to give an example. I'm from Kolkata where summers can get quite hot, but the humidity is even worse. However, we have a pretty old house with thick walls. My room has two 15 sqft windows and two 21 sqft doors. Room size is approximately 300 sqft which is cooled by a single 1.5 ton unit without any problems. In fact I've seen it run at 50 - 60% capacity except on the hottest of days where it operates close to its full power.
So you need to factor in all of these before you can size an AC appropriately. Try using one of those ac tonnage calculators online but be mindful of the fact that they typically oversell, at least from my experience. The recommended size for my room was 2 TR, but I'm happy with my decision of going with s smaller unit. Also, if your daily runtime is limited (say < 6 hours), you will probably not save much electricity cost with a inverter unit (variable speed) over a fixed speed unit.
